This invention relates to energy conversion, and, more particularly, to geokinetic energy conversion in which the earth is temperature modulated by solar radiation, and is used as a source or sink for heat. The term "geokinetic" refers to the fact that the geothermal energy of the invention varies by solar radiation.
The earth is a store of an almost inexhaustable amount of heat energy. Not only does the earth have a molten, i.e. geothermal, core which is at a relatively high temperature, it is continually being heated by the sun in a seasonally changing, i.e. kinetic, pattern.
Although the possibility of using both geothermal and solar energy has been known for many years, it has been difficult to do so in an efficient and economical manner. As a result, geothermal and solar energy largely have been ignored in favor of fossil fuels, which have been widely available at relatively low cost. Now that shortages are appearing and the cost of fossil fuels has increased, and is increasing, there have been renewed efforts to make use of both geothermal and solar energy.
In one of these efforts, a large hole is formed in the ground and filled with water. A heat exchange tube with a recirculatable fluid is immersed in the water and connected to a heat pump within a structure that is to be heated in winter, or cooled in summer. Heating and cooling are possible because a heat pump can be operated reversably. The water in the hole couples with the recirculatable fluid to the latent or potential heat of the earth. In the heating mode the heat extracted from the earth by the recirculatable fluid is released by the heat pump within the structure being heated. The converse takes place in cooling. The objection is that for efficient heat exchange the hole must be relatively large and deep. In addition, many solids will not support the required amount of water. In such a situation, an additional source of water is required to keep the system operating.
There is also the objection that the system tends to become saturated, i.e. less able to absorb or dissipate heat and thus less efficient, during long term operation. There is the further objection that additional energy such as that required for pumps is often needed to keep the large hole filled with water. In some cases an auxiliary source of water is required.
In an attempt to increase the efficiency of the waterhole system, water is circulated directly from the hole, instead of acting as a coupling between the earth and a recirculatable fluid. This method has many disadvantages. It requires frequent cleansing of the heat transfer surfaces and there is an intensified corrosion problem through continued agitation of the water from the hole. Again a significant amount of pump energy is required.
A related effort has made use of secondary heat exchanger pipes buried at a suitable depth in the ground. This approach uses fluid circulated through the pipes and then to a heat exchanger. The burying of the pipes eliminates the need for the digging of a large hole and filling it with water. But this technique generally produces a lower transfer of energy, and becomes progressively less effective, in part because of saturation, with sustained usage. Furthermore, the buried pipe must be of considerable length in order to achieve even marginal heat conversion for any sustained period. The need for a long pipe means that a large capacity pump must be used for even minimal water circulation.
Nevertheless, even when geothermal and solar methods are less economical than fossil fuels, they have the advantage of producing less environmental pollution.
Accordingly, it is an object of the invention to facilitate both the geothermal and solar conversion of energy. A related object is to achieve conversion efficiencies which approach those of fossil fuels. Another related object is to conserve on fossil fuels in both solid and fluid form.
A further object of the invention is to achieve geothermal and solar energy conversion with mitigation of the disadvantages that characterize prior systems. In particular, it is an object of the invention to increase the long term efficiency of coupling between the earth and a geothermal and solar conversion system. A related object is to increase the usefulness of prior geothermal and solar systems. Another related object is to achieve efficient geothermal and solar conversion of energy without the need for large-scale water filled holes, or the need for the circulation of potentially corrosive liquids. A further object is to overcome the disadvantage of geothermal systems employing long pipes.
A still further object of the invention is to enhance the performance of geothermal and solar piping systems. A related object is to reduce the saturation effect that has attended the use of such systems.